We've only explored a fifth of the world’s oceans – the remainder has never been seen by human eyes, or mapped.
But even so, we’ve found some weird and wonderful creatures, from anglerfish, with their glowing lures hanging over their faces, to narwhals, known as the unicorns of the sea.
But how much do YOU know about marine animals?
Our 15-question multiple-choice quiz will test your knowledge of sea life to the limit.
Don’t worry, we start off easy, with some very basic questions which you’ll probably know from general knowledge.
But stick with it, and there’s some very obscure details about denizens of the depths that only a true master of the deep will know.
* Can’t get enough trivia action? Check out our dedicated Yahoo Quizzes page for more brainteasers! *